1. Field of the Invention
This invention relates to a signal transmission method, a signal record (recording, recordable or recorded) medium and a signal reproducing apparatus applicable to prevention of copying or unauthorized use of transmitted or recorded and/or reproduced signals, or to a charging system.
2. Description of the Related Art
With promulgation and increased capacity of a digital record medium, such as an optical disc, prevention of copying and unauthorized use thereof is becoming crucial. That is, digital audio data or digital video data can be copied or dubbed to produce a non-deteriorated duplicate, while computer data can be easily copied to produce the same data as the original data. The result is that the copyright tends to be infringed by unauthorized copying.
With a view to preventing unauthorized copying, a standard for recording the information for preventing unauthorized copying on the record medium for original data has been proposed and used.
In an unauthorized copying preventing system in a digital audio signal recording/reproducing apparatus, termed a rotary head digital audio tape recorder (R-DAT), an inhibition code for inhibiting copying of digital data or inhibiting copying of a generation exceeding a pre-set number, that is for limiting the copying generation, or a so-called inhibition code of the standard of the serial copying management system (SCMS), is recorded in a main data area for digital audio signals recorded on a digital audio tape as a signal record medium. If this inhibition code is detected by the digital audio signal recording apparatus, the digital audio signals are prohibited from being recorded on a new digital audio tape.
For preventing copying of, for example, digital video signals, recorded on a signal record medium, it is also proposed in JP Patent Kokai Publication JP-A-6-44755 (1994) to record pre-set ID bits, that is the inhibition code of a standard for copying generation management system (CGMS), on an original digital record medium, as in the case of the above-mentioned system for prevention of unauthorized copying among recording/reproducing apparatus for R-DAT.
In the case of computer data, the file contents themselves are ciphered using the ciphering key information to permit use only by authorized registered users. This is pertinent to a system in which a digital record medium with information ciphered and recorded thereon is distributed as a form of information circulation, and the user acquires the key information for the contents he or she needs on payment of a prescribed fee for deciphering and using the computer data.
However, as shown in JP Patent Kokai Publication No. 5-173891 (1993), the above-mentioned ciphering key information or inhibition code for the signal record medium is recorded on a specified site on the record medium proper to the system and which is accessed by the user.
On the other hand, with playback mode information, such as copying management information or charging information, since bit allocation or the data position on the record medium is pre-fixed, there is a risk that the information will be skipped in reading or altered in use. In other words, since the playback mode information, such as the copying management information or the charging information, is at a user accessible area, it is likely to be decoded or illegally copied by a user having a malignant intention.
In addition, if the playback mode information is arrayed in a fixed manner in an optional place depending on the particular ciphering technique, interchangeability tends to be lost. If the playback mode information is arrayed fixedly, the ciphering technique is also fixed, so that it becomes poor in flexibility and extendibility, while durability of the format itself is likely to be lowered.
This problem is raised not only when recording/reproducing or transmitting/receiving digital signals but also when transmitting analog signals.